1. Field of the Invention
The present invention relates to a process for reclaiming a silicon wafer substrate from a semiconductor wafer for reusing the silicon wafer as control wafers.
2. Description of the Related Art
In modern semiconductor device technology, low-k dielectric material has been used to replace traditional silicon diode oxide as the inter-metal dielectric layers to improve the electrical performance of the semiconductor devices by suppressing signal-propagation delay, cross-talk between metal lines and power consumption due to their low dielectric constants. One of the promising low-k dielectric material is the trimethylsilane (TMS)-based dielectric material. The TMS-based dielectric material is an organosilicate glass with a dielectric constant as low as about 2.1.
Prior to forming a low-k dielectric layer on production wafers, the low-k dielectric layer usually is deposited on a control wafer to assure that physical and electrical characteristics of the low-k dielectric layer satisfy process requirements. Once these characteristics of the low-k dielectric layer deposited on the control wafer are verified to be within the desired range defined by the process specifications, the same recipe is used for the test wafer is set up to process the production wafers. After being processed, the control wafer must be transferred to a cleaning station where the low-k dielectric layer is removed and the control wafer's silicon substrate is recycled to be used again as a control wafer. This is also known as a reclaim procedure of control wafers.
FIG. 6 shows a cross-sectional view of a control wafer according to a conventionally known procedure for reclaiming control wafer. A traditional reclaim procedure of control wafers includes using HF or H2SO4 to remove the low-k dielectric layer. The traditional reclaim procedure results in residue 105 of the low-k dielectric material on the control wafer 100 as shown in FIG. 6. Residue 105 on the top surface of the control wafer 100 affects the deposition of low-k dielectric layers on the control wafer 100 during subsequent reuse of the control wafer 100. As a consequence, because the reclaimed control wafer substrate 100 is not representative of the virgin production wafer, the process recipe generated using the process parameters measured on the reclaimed control wafer would not be useful to run production wafers.
Other known methods involve removing the low-k dielectric layer from the control wafers by sandblasting or polishing. These mechanical removal process, however, remove some amount of the underlying silicon wafer substrate at each reclaim cycle and thus limit the number of times the control wafer substrate can be recycled.